States In 140Ce Research Articles

Direct determination of ground-state transition widths of low-lying dipole states in 140Ce with the self-absorption technique

The technique of self absorption has been applied for the first time to study the decay pattern of low-lying dipole states of 140Ce. In particular, ground-state transition widths Γ0 and branching ratios Γ0Γ to the ground state have been investigated in the energy domain of the pygmy dipole resonance. Relative self-absorption measurements allow for a model-independent determination of Γ0. Without the need to perform a full spectroscopy of all decay channels, also the branching ratio to the ground state can be determined. The experiment on 140Ce was conducted at the bremsstrahlung facility of the superconducting Darmstadt electron linear accelerator S-DALINAC. In total, the self-absorption and, thus, Γ0 were determined for 104 excited states of 140Ce. The obtained results are presented and discussed with respect to simulations of γ cascades using the DICEBOX code.

Decay pattern of the Pygmy Dipole Resonance in140Ce

The decay behavior of low-lying dipole states in 140Ce was investigated exploiting the γ3-setup at the HIγS facility using quasi-monochromatic photon beams. Branching ratios of individual excited states as well as average branching ratios to low-lying states have been extracted using γ – γ coincidence measurements. The comparison of the average branching ratios to QPM calculations shows a remarkable agreement between experiment and theory in the energy range from 5.0 to 8.5 MeV.

One-phonon octupole vibrational states in 136Xe, 137Cs, 138Ba, 140Ce and 142Nd with N = 82

Excited high spin states in 136Xe, 137Cs, 138Ba, 140Ce and 142Nd with N = 82 are reorganized and interpreted in terms of the weak coupling mode of an octupole 3− phonon. Nearly identical sequences of levels with ΔI = 3 and Δπ = yes built on 17/2+ and 23/2− states are found, for the first time, up to 29/2+ and 35/2−, respectively, for 22 states of 137Cs . Also, nearly identical sequences of levels with ΔI = 3 and Δπ = yes built on the 6+ and 9− states are found, for the first time, up to 14+ and 17−, respectively, for 18 states of 136Xe, up to 14+ and 17−, respectively, for 24 states of 138Ba and up to 11+ and 14−, respectively, for 14 states of 140Ce. New spins and parities are assigned, tentatively, to the high spin states of these nuclei based on the weak coupling mode of an octupole 3− phonon. The weak coupling of an octupole 3− phonon needs to be considered when single particle configurations are assigned to high spin states. Neutron particle-hole states (νh 11/2 −1 f 7/2 +1 ) with weak coupling of an octupole 3− phonon are proposed, for the first time. The νh 11/2 −1 f 7/2 +1 excitation energies (E ext(1p1h)) are nearly constant with increasing of Z. One-phonon excited states in 136Xe, 137Cs, 138Ba and 140Ce have the stretched weak coupling configurations of ΔI = 3. But one-phonon excited states in 142Nd show the non-stretched weak coupling configurations of an octupole phonon with ΔI = 3 and 2.

Some suggestions about the research of theE2(T=1) resonance excitation by (n, γ) reaction on cerium

Determining at microscopic level the interaction responsible for the excitation of collective states of140Ce makes it possible to use in a coherent way the direct-semidirect model in the study of the140Ce(\(\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\rightharpoonup}$}} {n} \), γ) reaction. Computations of differential cross-sections give useful pieces of information about the effects caused by the excitation of the isovector quadrupole giant resonance on the γ-ray emission geometry, closely connected with the polarization state of the incident neutron. Thus, the results supply helpful suggestions on a possible experimental research of theE2(T=1) excitation by means of the radiative capture reaction.

Excited states above the 6+ isomer in140Ce

An in-beam study of excited states in140Ce revealed 16 new levels of positive and negative parity on top of the 6+ isomer. The excitation energies of these states are well reproduced by diagonalizing the same Hamiltonian in two model spaces, aπ=+1 shell-model basis and aπ=−1 particle-core coupling basis.

On the M1 and M2 strengths in 140Ce

The available experimental and theoretical data on M1 and M2 states in 140Ce are analyzed. Comparison of the experimental form factors of inelastic scattering of electrons at 165° with DWBA calculations within the quasiparticle-phonon model shows that the experiment does not contradict the existence of noticeable M1 transitions in 140Ce.

Unelastische Streuung von 50 und 65 MeV-Elektronen an Ce, La und Pr

The reduced matrix elements for the ground state transitions to the first 2+, 3− and 4+ states in140Ce and14Ce were determined by DWBA analysis. In the giant resonance region of Ce, La and Pr three broad resonances at excitation energies of 9, 12 and 15 MeV have been found. They are interpreted asM1,E2 andE1 giant resonances. For Ce the total widths are (2.2±0.4) MeV (M1) and (2.8±0.3) MeV (E2) and the groundstate radiative widths (90±45) eV (M1), (100±30) eV (E2) and (5±1) · 104 eV (E1).

Analog states of 140La levels

Analog states in 140Ce have been studied through elastic and inelastic proton scattering on 139La in the energy range E p = 9–12 MeV. We have shown that the 14 first excited states of 140La can be described by the two configurations [ ( g 7 2 ) p ⊗ ( f 7 2 ) n ] and [ ( d 5 2 ) p ⊗ ( f 7 2 ) n ] according to the assumption of Kern et al. The elastic scattering results are in complete agreement with the 139La(d, p) ones. The study of the inelastic scattering to the 166 keV excited state of 139 La( d 5 2 level) , which gives a direct and sensitive test of the [ ( d 5 2 ) p ⊗ ( f 7 2 ) n ] components, has confirmed that only these two configurations are important and that the relative intensities of the two configurations deduced from (d, p) experiments are correct. On the other hand, the two sets of theoretical wave functions which exist are not able to reproduce experimental results. We are able to confirm that the proton peak observed at E p = 10.3 MeV in the 140Ce(e, e'p) 139La reaction by Shoda et al. corresponds to the analog of the 1 − state at 466 keV in 140La.

Generalized neutron particle-hole states in the N = 82 isotone 142Nd

Angular distributions for the inelastic proton decay of the two lowest isobaric analogue resonances in 143Pm ( J π = 7 2 − , 3 2 − ) have been measured. Proton decay widths and excitation energies for levels in 142Nd between E x = 3 MeV and 5 MeV are deduced. Most of the observed levels can be interpreted as generalized neutron particle-hole (GNPH) states, a concept to which physical significance has been given by a similar experiment on 140Ce. Level spacings of the GNPH states as well as partial widths and angular distributions of decay protons from corresponding J π = 7 2 − and 3 2 − resonances are found similar for the different N = 82 isotones. The wave functions of four prominent states in 142Nd are determined in terms of GNPH configurations | lj −1, J π 〉 with lj = d 3 2 , s 1 2 , d 5 2 and J π = 7 2 − and 3 2 − . The wave functions of these states are similar to those of corresponding states in 140Ce. The spin splitting of the lowest GNPH configuration ¦d 3 2 − , 7 2 −ĭs identical for both N = 82 nuclei within the uncertainties of the analysis. This shows that the interaction among GNPH configurations depends only weakly on the number of protons. This fact is used to assign spins 1 − and 2 − to states containing appreciable amounts of the configuration | s 1 2 − , 3 2 − 〉

Spins of generalized neutron particle-hole states in 140Ce with excitation energies above Ex=4 MeV

Spins are assigned to states in 140Ce observed in the proton decay of resonances which are the isobaric analogues of the first (J π= 3 2 −) , second (J π= 1 2 −) and fifth (J π= 5 2 −) excited states in 141Ce. Spins 2 −, 1 −, 2 −, 2 − and 1 − are assigned to the states at E x = 4.158, 4.182, 4.580, 4.748 and 4.77 MeV in 140Ce, respectively. The states at E x = 5.026, 5.196, 5.424 and 5.466 MeV are shown to have spins 2 − or 3 −. The assignments are based on the assumption that only the generalized neutron particle-hole configurations | d 3 2 −1⊗ 141 Ce(Jβ)〉 and | s 1 2 −1 ⊗ 141 Ce (Jβ)〉 contribute to the proton widths measured on the resonance Jβ.

Structure of generalized neutron particle-hole states in 140Ce

Inelastic proton scattering on 140Ce via the 7 2 − g.s. isobaric analogue resonance in 141Pr is analysed. The states at E x = 3.402, 3.478, 3.710, 3.792, 3.912, 4.000 and 4.538 MeV in 140Ce are interpreted as generalized neutron particle-hole (GNPH) states with the spins J π = 4 −, 3 −, 5 −, 3 −, 2 −, 4 − and 3 −, respectively. Their wave functions are determined in terms of GNPH configurations. In the seven states, the strengths of the GNPH configurations ∣s 1 2 −1⊗ 141 Ce (g.s., 7 2 − )〉 and ∣ d 3 2 −1⊗ 141Ce (g.s., 7 2 − )〉 are found almost completely. Their centres of gravity are determined.

Generalized neutron particle-hole states in 140Ce

Angular distributions for the inelastic proton decay of the low-lying isobaric resonances in 141Pr have been measured at bombarding energies between E p = 9.40 and 11.65 MeV. Characteristic groups of particle-hole states in 140Ce are observed on each resonance. The excitation functions for these groups show a negligible non-resonant background. Excitation energies and proton decay widths are determined for states in 140Ce up to E x = 5.5 MeV. The concept of a generalized neutron particle-hole (GNPH) configuration is introduced. Most of the observed states are found to consist of the GNPH configurations |( d 3 2 −1, Jβ) I − 〉 and |( s 1 2 −1, Jβ) I − 〉 mainly. The mixing of the GNPH configurations with other configurations turns out to be weak.

Identification of 1 − neutron particle-hole states in 140Ce

The γ-ray decay of neutron particle-hole states in 140Ce has been studied with the reaction 140Ce(p,p′γ o) 140Ce. Evidence is presented that the strong ground-state γ rays observed from some of these states are E1 transitions. This allows the identification of 1 − states.